Common Causes of Electric Motor Failure

Motors are commonly used all around industrial environments. They are also becoming more technical and complex, making it a challenge to ensure they remain working as they should. The causes of driving issues and motor issues are not confined to one single domain of expertise. Both electrical and mechanical issues can cause motor failure.

It is important to arm yourself with the appropriate knowledge when it comes to electric motor failure.

Electric Motor Failure Causes

Transient Voltage

Transient voltages can arise from many different sources, whether outside or inside of the plant. Transient voltages can be generated from adjacent loads turning on or off, power factor correction, capacitor banks, or distant weather. Transients can also come in varying degrees of frequency and amplitude, causing the insulation to break down in motor windings and may even erode parts.

Voltage Imbalance

An imbalance in impedance or load distribution can cause an imbalance across the three phases of the distribution system. Some causes may be embedded in the cabling to the motor, the windings themselves, or the terminations at the motor. This imbalance can cause damage in each of the circuit phases.

Harmonic Distortion

Harmonics are unwanted additional sources of high-frequency energy. This additional energy is not used to turn the motor shaft and instead rotates inside of the windings, causing energy losses internally. These losses disappear in the form of heat. Over time, they will deteriorate the insulation capacity of the windings.

Reflections on Drive Output PWM Signals

Variable frequency drives utilize a pulse width modulation that controls the output voltage and frequency of a motor. If there is a resistance between the source and load, reflections will be generated. They may also result from improper insulation, equipment degradation over time, or improper component selection.

Sigma Currents

These currents are considered stray currents that rotate in a system. These currents are designed as a result of the voltage level, signal frequency, inductance, and capacitance in conductors. These rotating currents can make their way through protective earth systems, causing problems. In some cases, they can even cause excess heat in windings. These currents can be found in the motor cabling and are considered the sum of the current of the three phases at any single point in time.

Operational Overloads

Motor overload happens when a motor is under an imprudent load. The main signs of motor overload are insufficient torque, excessive current draw, and overheating. Excessive motor heat also results in motor failure. In some cases, the motor will continue to run hot, even though other motor components such as the bearings, and windings may work just fine.  

Additional causes of electric motor failure include:

• Misalignment
• Shaft imbalance
• Shaft looseness
• Bearing wear
• Soft foot
• Pipe strain
• Shaft voltage

Success Strategies

Electric motor repair is crucial if you are experiencing motor failure. However, to prevent or restore premature failures, you can try these four strategies:

• Document operating condition
• Capture and document important measurements during installation, before, and after maintenance
• Create an archive reference of measurements to help facilitate trend analysis
• Plot individual measurements to establish a baseline trend

Categorised in: AC Electric Motors

This post was written by admin